The Phosphates of America. 93 



Volumes might still be devoted to a discussion of the reactions 

 which go on between the gases in the chambers, and, from a truly 

 scientific point of view, few questions are of a more absorbingly 

 interesting nature. Our present purpose, however, of pointing out 

 how to avoid accidents or trouble in what is really, when properly 

 understood, a very simple and natural process, will best be served 

 by briefly summarizing a few leading facts. 



The nitric acid used in the process plays no other part, as we 

 have previously explained, than that of carrying from the oxygen 

 of the air to the sulphurous acid, the necessary atom of the former 

 by which, with water, its transformation into sulphuric acid is 

 effected, and consequently whatever be the manner of its entry, it 

 is eventually discharged from the chambers in its original form. 

 This being allowed, it becomes immaterial whether ic is intro- 

 duced directly and separately into the chambers, as is customary 

 in many large European works, by means which have frequently 

 been described, or whether it is sent in by the older, more econom- 

 ical, and certainly simpler system of "potting." 



If the gases reach the chambers with a due excess of oxygen 

 and there meet with a sufficiency of steam, none of the nitrogenous 

 compounds will disappear. 



Should steam, however, be absent, there must naturally be 

 formed a nitro-sulphuric compound, which will prevent any reac- 

 tion between the sulphurous acid and the oxygen by using up the 

 nitrogen for its own condensation. 



If the entering gases are deficient in oxygen, no sulphuric acid 

 can be formed, owing to the fact that -the nitrogen compounds are 

 reduced in rapid succession to bioxide and protoxide. If, on the 

 other hand, they contain too little sulphurous acid, the nitrogen 

 compounds are transformed into nitric acid by the steam, and in 

 this state exercise a violent and destructive action on the lead. 



With the display of only ordinary care and intelligence, how- 

 ever, there should be little chance for any of these mishaps, and a 

 simple glance at regular intervals through the side windows or a 

 slight removal of the caps will always insure against them. 



The gases in the first working chamber must invariably be 

 white, while those issuing from the last cap of the second chamber 

 must be of a very deep red and emit strong nitrous fumes. 



We know from experience that the gases allowed to pass away 

 from well-managed factories do not contain more than a maximum 

 of five per cent, of oxygen, and we also know that when the red 



